Fluorocarbon elastomers are synthetic elastomeric polymers with a high fluorine content. See, for example, W. M. Grootaert et al., "Fluorocarbon Elastomers", Kirk-Othmer, Encyclopedia of Chemical Technology, Vol 8, pp. 900-1005 (4th ed., John Wiley & Sons, 1993). Fluorocarbon elastomers, particularly the copolymers of vinylidene fluoride (VF2) with other ethylenically unsaturated halogenated monomers, such as C.sub.3 F.sub.6 (hexafluoropropylene or HFP), have become the polymers of choice for high temperature applications, such as seals, gaskets, and linings, especially when shaped articles thereof are subject to exposure to aggressive or harsh environments, such as solvents, lubricants, and oxidizing or reducing conditions. See, for example, U.S. Pat. No. 4,912,171 (Grootaert et al.), which discloses a fluoroelastomeric polymer prepared from VF2, tetrafluoroethylene (TFE), and a copolymerizable hydrocarbon olefin.
A major drawback to many applications of shaped articles made of such fluorocarbon elastomers has been their inability to satisfactorily function at low temperatures. Typically, at temperatures only slightly below 0.degree. C., shaped articles made from copolymers of VF2 and HFP become stiff and fail to perform satisfactorily.
Low temperature flexibility of VF2 elastomers may be improved by substituting perfluoro(allyl vinyl ethers) for the HFP in VF2/HFP/TFE copolymers as discussed in U.S. Pat. No. 5,214,106 (Carlson et al.). Polymers of perfluorovinyl ethers or copolymers with LTE are also discussed in U.S. Pat. No. 3,817,960 (Resnick).
Cured perfluoroelastomers may be provided that exhibit enhanced low temperature properties through the incorporation by conventional compounding techniques of a selected perfluoropolyether into the perfluoroelastomer compound as discussed in U.S. Pat. No. 5,268,405 (Ojakaar et al.). A higher than normal loading of such additives may be accomplished by using a compatibility extender such as discussed in U.S. Pat. No. 3,632,788 (Stivers et al.). These additives are not permanently incorporated into the polymers and can be lost during post treatment and use of the shaped articles.
Many other fluorinated ethers have been described in the literature. One type is characterized by one of several homopolymeric segments or blocks of repeating units of the formula --CF(CF.sub.3)CF.sub.2 --O-- made from hexafluoropropylene oxide. Another type is that characterized by blocks of repeating units of the formula --CF.sub.2 CF.sub.2 --O-- made from tetrafluoroethylene oxide. Others, made by reacting oxygen with tetrafluoroethylene or hexafluoropropylene, are characterized by a backbone of repeating --CF.sub.2 O--, --CF(CF.sub.3)CF.sub.2 O--, or --CF(CF.sub.3)O-- units, a backbone of randomly distributed --CF.sub.2 O-- and --CF.sub.2 CF.sub.2 O-- units, a backbone of --CF(CF.sub.3)CF.sub.2 O-- and --CF.sub.2 CF.sub.2 O--units and optionally a, --CF.sub.2 O-- and --CF(CF.sub.3)O-- units. Another type of fluorinated ether is that characterized by backbone units of the formula --(CF.sub.2).sub.a O(CF.sub.2).sub.b -- made by photopolymerization.
A peroxide-vulcanizable, fluorine-containing elastomer can be attained by copolymerizing a perfluoro(vinylether) compound represented by the general formula: CF.sub.2.dbd.CFO(CF.sub.2 CF(CF.sub.3)O).sub.m (CF.sub.2).sub.n X, wherein X is a bromine atom or an iodine atom and m and n each are 1, 2 or 3; and a fluorine-containing olefin having 2 to 8 carbon atoms in the presence of an iodine and bromine-containing compound represented by the general formula: RBr.sub.n I.sub.m, wherein R is a fluorohydrocarbon group, a chlorofluorohydrocawbon group, a chlorohydrocarbon group or a hydrocarbon group, and n and m each are 1 or 2 as disclosed in U.S. Pat. No. 5,225,504 (Tatsu et al.).
None of these materials, however, have sufficient low temperature flexibility, particularly flexibility at temperatures as low as -50.degree. C. or lower.